The family typically doesn't know what's going to happen because they are sent off on a vacation for a week. While they're gone, a team of designers, contractors, and hundreds of workers usually demolish the old house and build a brand new one.
For anyone who hasn't seen the show, these replacement homes are not your standard 2,000-square-foot tract homes. They're usually 4,000-square-foot (or more) luxury residences that boast every kind of convenience. The challenge is to get the house built, furnished, and landscaped during the family's seven-day vacation. It may sound impossible, but somehow it gets pulled off every week.